Method of Flow Drill Screwing Parts

ABSTRACT

A method of fastening a plurality of parts together with a flow drill screw. An indentation is formed on one side of a first part and a second part is assembled into engagement with the side of the first part with the indentation facing the second part. The flow drill screw is inserted through the indentation and material is displaced from the part into a void defined by the indentation. Two or more panels or parts may be joined by aligning a flow drill screw with voids formed by indentations that are formed by embossing one or more panels.

TECHNICAL FIELD

This disclosure relates to a method of fastening parts together with aflow drill screw in a flow drill screwing operation.

BACKGROUND

Flow drill screwing is a one-sided joining technique that can beutilized to secure lightweight materials and dissimilar materialstogether. Many other mechanical fastening technologies, such asself-piercing rivets or clinching, are two sided joining methods, andhence require greater access to the components for joining Regardless ofthe joining method, it is desirable to have mating parts flush and avoidor minimize gaps between the parts to insure a robust and high qualityjoint.

Flow drill screwing joins parts together by inserting the screw directlyonto the surface of the assembly. The screw is rotated at a high speedof, for example, 3000-5000 rpm and a force in the range of to two tofour kilo-newtons to cause localized heating of the components forjoining. After sufficient heating, the screw penetrates the surface andan extruded boss is formed on the opposite side of the joint. The tip ofthe screw is then rotated at a lower speed of, for example, 500 to 2000rpm to create a thread rolled surface. The speed of rotation is thenfurther reduced to drive the screw to the seated position.

While the flow drill screwing process may be performed with or without aclearance hole, when parts are joined without a clearance hole, materialtends to flow into the area between the parts. Material that flows intothe area between the parts can cause separation of mating parts fromeach other. Hence, a gap may be created between the parts as a result ofthe material that flows between the parts that are joined together. Suchgaps between the joined parts are likely objectionable.

This disclosure is directed to the above problems and other problemsencountered when joining parts together in a flow drill screwing processparticularly when no clearance hole exists prior to performing the flowdrill screwing process.

SUMMARY

According to one aspect of this disclosure, a method of fastening aplurality of parts together is disclosed that comprises forming anindentation on a side of a first part, assembling a second part intoengagement with the side of the first part with the indentation facingthe second part, and inserting a flow drill screw into the first partand second part through the indentation.

According to other aspects of the method, material is displaced from thefirst or second part into the indentation. The method may furthercomprise assembling a third part to the second part and inserting theflow drill screw into the third part. According to the method, theindentation may be a first indentation and the method may furthercomprise forming a second indentation on a second part and whereinduring the assembling step the first and second indentations are alignedwith each other. The forming step may further comprise an embossingstep.

According to another aspect of the disclosure a pre-assembly is providedthat includes a first part that is an uninterrupted plate that does notinclude a pilot hole, a second part that is an uninterrupted plate thatdoes not include a pilot hole, and a flow drill screw oriented forinsertion into the first part at a location, wherein one of the firstpart and the second part define an embossed void on an internal sidethat faces the other of the first part or second part, and wherein theembossed void is aligned with the flow drill screw.

According to other aspects of the pre-assembly, the embossed void may beprovided on the first part. Alternatively, the embossed void may beprovided on the second part. The embossed void may include two embossedvoids with a first embossed void provided on the first part and a secondembossed void provided on the second part. Instead of an embossed void,the void could be formed by machining to remove material from the voidarea.

According to another aspect of the disclosure, an assembly is providedthat comprises a first part having a first facing surface, a second parthaving a second facing surface that is assembled against the firstfacing surface of the first part, and a flow drill screw extendingthrough the first part and the second part. One of the first and secondparts defines a void between the parts through which the flow drillscrew is inserted and, wherein material from the first part istransferred into the void when the flow drill screw is inserted throughthe first part.

According to other aspects of the disclosure, the assembly may furthercomprise a third part that is assembled to a first facing surface of thesecond part. The third part may define a void between the second partand the third part. The void may be defined by the first part and/or thesecond part.

The above aspects of the disclosure and other aspects will be betterunderstood in view of the attached drawings and detailed description ofthe illustrated embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary perspective view of an embossing tool and a partafter an area of the part is embossed;

FIG. 2 is a fragmentary cross-section perspective view of two partsassembled together with a void, or indentation, formed by embossing oneof the parts;

FIG. 3 is a cross-sectional view of a flow drill screw in position abovetwo parts assembled together with a void formed by embossing the secondfacing surface of the second part;

FIG. 4 is a cross-sectional view of a flow drill screw joining two partsassembled together with a void formed by embossing the second part;

FIG. 5 is a cross-sectional view of a flow drill screw in position abovetwo parts assembled together with a void formed by embossing the firstfacing surface of the upper part;

FIG. 6 is a cross-sectional view of a flow drill screw joining two partsassembled together with a void formed by embossing the upper part;

FIG. 7 is a cross-sectional view of a flow drill screw in position abovetwo parts assembled together with a void formed by embossing the firstfacing surface of the upper part and the second facing surface of thesecond part;

FIG. 8 is a cross-sectional view of a flow drill screw joining two partsassembled together with a void formed by embossing the first facingsurface of the upper part and the second facing surface of the secondpart;

FIG. 9 is a cross-sectional view of a flow drill screw in position abovethree parts assembled together with a void formed by embossing the firstfacing surface of the upper part and the first facing surface of theintermediate part, and the second facing surface of the third part; and

FIG. 10 is a cross-sectional view of a flow drill screw joining threeparts assembled together with a void formed by embossing the firstfacing surface of the upper part and the second facing surface of thethird part.

DETAILED DESCRIPTION

A detailed description of the illustrated embodiments of the presentinvention is provided below. The disclosed embodiments are examples ofthe invention that may be embodied in various and alternative forms. Thefigures are not necessarily to scale. Some features may be exaggeratedor minimized to show details of particular components. The specificstructural and functional details disclosed in this application are notto be interpreted as limiting, but merely as a representative basis forteaching one skilled in the art how to practice the invention.

Referring to FIG. 1, an embossed panel 10, or part, is shown with aembossing tool 12 used to form an indentation 16 on the embossed panel10. As used herein, the term “embossed” refers to forming an indentationin the surface of an object such as a panel 10, or part. While the term“debossed” could be used to refer to an indentation that is inverted,for simplicity, the term embossed is used for either case. Further, theterms “top” and “lower” are used to refer to the parts and surfaces asillustrated and it should be understood that the parts may be arrangedin any orientation in actual production, such as sideways, angularlyoriented, or even inverted with the first part being above the secondpart.

Referring to FIG. 2, the embossed panel 10 is shown with a flat panel 18that are assembled together to define a void 22 in the location of theindentation 16. A first facing surface 26 of the flat panel 18 and asecond facing surface 28 of the embossed panel 10 define the area of thevoid 22. A protrusion 30 is formed on the opposite side of the embossedpanel 10 from the indentation 16 as a result of the displacement ofmaterial caused by the embossing tool 12 forming the indentation 16 inthe embossed panel 10. The void 22 could also be machined in aconventional machining process in which material is removed from thearea that is to receive the flow drilling screw and if so no protrusion30 would be formed.

Referring to FIG. 3, a flow drill screw 32 is shown to have an axis 36that corresponds to the rotational axis of the flow drill screw 32. Theflow drill screw 32 includes a head 38 and may also include a flange 40.The flange 40 increases the area on the flat panel 18 that is covered bythe flow drill screw 32. A screw tip 42 is provided on the flow drillscrew 32 at the end of a threaded shaft 46.

As shown in FIG. 3, the flow drill screw 32 is shown disposed with theaxis 36 aligned with the void 22 formed by assembling the embossed panel10 to a flat panel 18. The first facing surface of the flat panel 18 andthe second facing surface 28 of the embossed panel 10 are shown adjacentto and engaging each other.

Referring to FIG. 4, a cross section of the flow drill screw 32 joiningthe flat panel 18 and the embossed panel 10 together is shown in crosssection. A flow cavity 48 is formed in the head 38 that may also extendinto the flange 40 of the flow drill screw 32. The screw tip 42 of theflow drill screw 32 is shown extending outwardly from the embossed panel10. The threaded shaft 46 of the flow drill screw 32 is shown engagingthreads that are rolled into the sides of the openings formed in thepanels 10 and 18 by insertion of the flow drill screw 32. Reverse flowmaterial 50 is received within the flow cavity 48 as the flow drillscrew 32 is inserted into the panels 10 and 18. Forward flow material 52flows through the reverse side 54 of the embossed panel 10. Intermediateflow material 56 flows into the void 22 defined between the embossedpanel 10 and the flat panel 18.

Referring to FIGS. 5 and 6, an alternative embodiment is shown in whichan inverted embossed panel 60 is provided with an inverted indentation62. The same reference numerals are used to refer to the flow drillscrew 32 and the other similar elements in the embodiments of FIGS. 5-10that were used to describe the embodiments of FIGS. 1-4.

Referring to FIG. 5, the flow drill screw 32 is shown with its axis 36aligned with the void 22 defined by the inverted indentation 62 in theinverted embossed panel 60 and the flat panel 18.

As shown in FIG. 6, the flow drill screw 32 is shown inserted throughthe inverted embossed panel 60 and the flat panel 18. Reverse flowmaterial 50 and the protrusion 30 shown in FIG. 5 are shown having beendisplaced into the flow cavity 48 formed by the head 38 and flange 40 ofthe flow drill screw 32. In the void 22, shown in FIG. 4, intermediateflow material 56 is shown that is displaced from the flat panel 18.Additional material flows as forward flow material 52 outwardly from thereverse side 54 of the flat panel 18.

Referring to FIG. 7, a flow drill screw 32 having an axis 36 is showndisposed over an inverted embossed panel 60 and a embossed panel 10. Theinverted embossed panel 60 defines an inverted indentation 62. Theembossed panel 10 includes an indentation 16. The indentation 16 andinverted indentation 62 together form a double void 66 between theembossed panel 10 and the inverted embossed panel 60. The protrusions 30are formed when the indentations 62 and 16 are formed in the respectivepanels.

Referring to FIG. 8, a flow drill screw 32 is shown inserted in embossedpanel 10 and inverted embossed panel 60 (shown in FIG. 7). The flowdrill screw 32 is shown fully inserted through the panels 10, 60.Reverse flow material 50 is shown received within the flow cavity 48, aspreviously described. Forward flow material 52 is shown extending fromthe opposite side of the embossed panel 10. Intermediate flow material56 flows into the double void 66.

Referring to FIG. 9, another alternative embodiment is shown in whichtwo inverted embossed panels 60 are shown with the protrusion 30 of theinverted embossed panel 60 being received in the inverted indentation 62of the upper inverted embossed panel 60, as shown in FIG. 9. Theembossed panel 10 is shown below the two inverted embossed panels. Theflow drill screw 32 has an axis 36 that is shown aligned with theindentation 62 in the inverted embossed panel 60 and the indentation 16in the embossed panel 10. A double void 66 is defined between theembossed panel 10 and the lower inverted embossed panel 60. When theflow drill screw 32 is inserted through the three panels shown in FIG.9, material displaced during the flow drill screwing process accumulatesin flow cavity 48 defined in the head 38 and flange 40 of the flow drillscrew 32. Forward flow material 52 again is moved through the outboardside of the embossed panel 10 and material displaced during the flowscrew drilling process also accumulates within the double void 66.

Referring to FIG. 10, another alternative embodiment is shown in whichan inverted embossed panel 60 is assembled to a flat panel 18 and aembossed panel 10. The flow drill screw 32 has rotational axis 36 thatis aligned with the void 22 defined by the indentation 16 in theembossed panel 10 and the inverted void 68 defined by invertedindentation 62 in the inverted embossed panel 60. A protrusion 30 isformed on the top of the inverted embossed panel 60. Protrusion 30 isalso formed on the embossed panel 10 on the opposite side from theindentation 16.

In each of the above cases, the indentation 16 and the invertedindentation 62 define voids 22, double voids 66 or inverted voids 68that are intended to receive material formed when the flow drill screw32 is inserted through the panels 10, 60 without forming a pilot hole.The material accumulating in the voids 22, 66 and 68 are received in thevoids and does not tend to separate the panels that the flow drill screw32 is intended to join. According to the disclosed process, unwantedspacing or gaps between panels is avoided. While joining two panels andthree panels is illustrated, it is believed that the invention may alsobe applicable to four or more panels and also to parts that are notsheet metal panels. For example, the process may be applied to joining asheet metal panel to a cast part or the like without the departing fromthe disclosed concept.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms of the invention. Rather,the words used in the specification are words of description rather thanlimitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the invention.Additionally, the features of various implementing embodiments may becombined to form further embodiments of the invention.

What is claimed is:
 1. A method of fastening a plurality of partstogether comprising: forming an indentation on a side of a first part;assembling a second part into engagement with the side of the first partwith the indentation facing the second part; and inserting a flow drillscrew into the first part and second part, wherein the screw extendsthrough the indentation.
 2. The method of claim 1 further comprisingdisplacing material from the first or second part into the indentation.3. The method of claim 1 further comprising assembling a third part tothe second part and wherein in the step of inserting the flow drillscrew further comprises inserting the flow drill screw into the thirdpart.
 4. The method of claim 1 further comprising forming a secondindentation on the second part and wherein during the assembling stepthe second part is assembled to the first part with the indentation onthe side of the first part aligned with the second indentation.
 5. Themethod of claim 1 wherein the forming step is an embossing step.
 6. Themethod of claim 1 wherein the forming step is a machining step.
 7. Apre-assembly comprising: a first part that is an uninterrupted platethat does not define a clearance hole; a second part that is anuninterrupted plate that does not define a clearance hole; and a flowdrill screw oriented for insertion into the first part at a location,wherein the first part or the second part define an embossed void on aninternal side that faces the other of the first part or the second part,wherein the embossed void is aligned with the flow drill screw.
 8. Thepre-assembly of claim 7 wherein the embossed void is provided on thefirst part.
 9. The pre-assembly of claim 7 wherein the embossed void isprovided on the second part.
 10. The pre-assembly of claim 7 wherein afirst embossed void provided on the first part and a second embossedvoid is provided on the second part, and wherein the first embossed voidand the second embossed void are provided on first and second internalsides of the first part and the second part.
 11. An assembly comprising:a first part having a first facing surface; a second part having asecond facing surface that is assembled against the first facing surfaceof the first part; and a flow drill screw extending through the firstpart and the second part, wherein one of the first and second partsdefines a void between the parts through which the flow drill screw isinserted and, wherein material from the first or second part istransferred into the void when the flow drill screw is inserted throughthe assembly.
 12. The assembly of claim 11 further comprising a thirdpart that is assembled the second part.
 13. The assembly of claim 12wherein the third part defines a void between the second part and thethird part.
 14. The assembly of claim 11 wherein the void is defined bythe first part.
 15. The assembly of claim 11 wherein the void is definedby the second part.
 16. The assembly of claim 11 further comprising athird part that is assembled between the first part and the second partand wherein the first part defines a first void with the third part andthe second part defines a second void with the third part, and whereinmaterial is transferred into the first void and the second void when theflow drill screw is inserted into the assembly.